1. Field of the Invention
This invention relates to a method of preparing coupler dispersions for photographic use and more particularly, to a method of preparing extremely fine size coupler dispersions.
2. Description of Related Art
Copending application Ser. No. 631,607 entitled "Color Photographic Element", filed Dec. 21, 1990 by a number of the same applicants as this application and assigned to the same assignee as this application discloses a particular color photographic element wherein the image-dye forming couplers of certain layers are in a dispersion having a mean particle size of less than 0.14 microns. One of the advantages at least partially attributable to utilizing coupler dispersions of reduced particle size is that photographic elements employing such coupler dispersions exhibit reduced granularity.
U.S. Pat. No. 4,385,110 issued May 24, 1983, teaches that in order to make the particle size of an emulsion dispersion finer, it is usually necessary to use an emulsifying agent in a large amount. The use of an emulsifying agent in a large amount is liable to cause coating troubles due to foaming of the emulsion, such as the formation of pin holes, unevenness in the coated film thickness, and to deteriorate the film quality of the coated photographic element of a light-sensitive material.
In the manufacture of dispersions for use in photographic light-sensitive elements, such as coupler dispersions, the photographic coupler is dissolved in a permanent coupler solvent with the addition of an auxiliary coupler solvent that assists in the dissolution of the coupler in the permanent coupler solvent. This solution is mixed under high shearing action with an aqueous hydrophilic colloid, generally gelatin, containing a surfactant at elevated temperatures in order to break the organic phase into sub-micron droplets dispersed in the continuous aqueous phase. The auxiliary coupler solvent is then removed from the aqueous dispersion. Two techniques are employed for removing the auxiliary coupler solvent and these techniques depend upon the characteristic of the auxiliary coupler solvent. When the auxiliary coupler solvent is of low volatility, it is generally removed by evaporative techniques. When the auxiliary coupler solvent is less volatile, but at least partially water soluble, it is removed by washing by any suitable technique such as noodling coupled with washing as disclosed in U.S. Pat. Nos. 2,322,027; 2,801,170; 2,801,171; 2,949,360; and 3,396,027. Another suitable technique to employ is a membrane wherein the dispersion is contacted across the membrane as disclosed in copending U.S. application Ser. No. 516,955 filed Apr. 30, 1990, which application is assigned to the same assignee as this application.
There is a need for a simplified method of making photographic coupler dispersions wherein the particle size of the coupler dispersion is reduced from those techniques presently employed in the art.